Steam turbines and their design problems are, in particular, presented in Prof. Dr.-Ing. H.-J. Thomas, “Thermische Kraftanlagen” [Thermal Power Installations], 2nd Edition, 1985, Springer-Verlag. Details for calculating the enthalpy and further thermodynamic parameters can, for example, be extracted from “Technische Formeln für die Praxis” [Technical Equations for Practical Use], 24th Edition, 1984, VEB Fachbuchverlag, Leipzig.
Further reduction in the starting times of steam turbines is continuously required. Shorter starting times can only be achieved if all stages have, as far as possible, the largest possible mass flow admitted to them at the same time. It is only by this admission that the preheating of the steam turbine necessary for the shortest possible starting time can be achieved. The power generated by the turbine due to the mass flow being admitted must not, however, exceed the idling load. If the idling load is exceeded, uncontrolled increases in the rotational speed of the steam turbine can occur. The total mass flow which can be supplied overall is, therefore, limited.
High windage powers occur at the exhaust-steam end of the high-pressure stage (HP stage) during idling or low-load operation. These high windage powers lead to high temperatures at the exhaust steam end. A large part of the mass flow must therefore be supplied to the high-pressure stage in order to prevent unallowably high temperatures. The low-pressure stage (LP stage), however, also demands a comparatively high mass flow, in particular where large low-pressure stage cross sections and new materials, for example titanium for the blading of the low-pressure stage, are employed. The medium-pressure stage (MP stage) also requires a part of the mass flow.
If the necessary, high mass flow is admitted to both the high-pressure stage and the low-pressure stage, the overall power generated is distinctly located above the idling power. Attempts have therefore been made to adjust the distribution of the mass flows, by use of preliminary calculation, in such a way that idling operation becomes possible. In this case, the mass flows through the high-pressure stage and the medium-pressure/low-pressure stage were distributed in such a way that the power was not located above the idling power required.
It was only overheating of the high-pressure stage which was avoided by monitoring the temperature occurring at the exhaust-steam end. Only a small mass flow was left for the medium-pressure/low-pressure stage. If the mass flow for the medium-pressure/low-pressure stage was not sufficient or if the temperature at the exhaust-steam end of the high-pressure stage exceeded a specified value, rapid partial shut-down of the high-pressure stage was initiated. In consequence, the high-pressure stage, at least, was only inadequately preheated. Because of this inadequate preheating, a longer starting time was necessarily involved.